The present invention is related to co-pending U.S. patent application Ser. No. 395,108 entitled "Method and Apparatus for Identification of Articles", which is assigned to the present assignee.
Zirconium tubes generally are utilized to contain uranium oxide pellets for nuclear reaction processes. Specifically, uranium pellets are disposed in a zirconium tube, and the tube is sealed at both ends. In operation, the uranium filled zirconium tubes are lowered into water and energy is created due to a chain reaction fissioning of the uranium. The water serves as a necessary moderator of the fission neutrons and as a coolant. The uranium, however, should never be in direct physical contact with the water, otherwise the water becomes contaminated and the reactor must be shut down. The zirconium tubes provide this separation and are the first barrier for the containment of contaminating radiation. Thus, manufacture process control of zirconium tubes is very important. If tube defects can be quickly detected during the manufacturing process, then the cause of the defect can be determined and corrected.
A process for manufacture of zirconium tubes utilized in nuclear reactor processes is commonly referred to as a cold pilger mill process. In this pilger mill process, an ingoing zirconium tube is elongated stepwise over a stationary mandrel. The mandrel is tapered in the direction of rolling. Two grooved rolls, which embrace the tube from above and below, roll over the tube for a predetermined length, sometimes referred to herein as the "pass length".
The rolls receive a reciprocating lateral movement from a saddle in which they are mounted. At the same time, a reciprocating rotary movement is imparted to the rolls by pinions mounted on roll shafts. The reciprocating stroke of the saddle plus rolls is effected by a crank drive.
Grooves in the two rolls form a circular shaped pass which corresponds to the cross section of the ingoing tube. This pass tapers smoothly over a predetermined length of the roll circumference until it reaches the size of the "finished" tube diameter. In this way, the ingoing tube is worked to a desired degree as the rolls carry out their reciprocating movement. The elongation of the ingoing tube to the "finished" tube is effected through reductions in the diameter and wall thickness of the ingoing tube. This is due to the shape of the mandrel and pass which taper from the size of the ingoing tube to the size of the "finished" tube. The length of the tube section reduced per stroke depends on the length of the working pass.
More information regarding the cold pilger process is included in "Machinery and Equipment for the Manufacture of Tubes Using the Cold Pilger Process", Mannesmann Demag Huttentechnik, Zweigniederlassung der Mannesmann Demag AG, Subdivision MEER, Postfach 365, Ohlerkirchweg 66, D-4050 Monchengladbach 1, Fed. Rep. of Germany.
With known processes, once a "finished" tube is formed, the tube is cut and cleaned. Sometimes it also is necessary to straighten the tube. The tube is then inspected for defects. Generally, the process steps of cutting, cleaning, straightening, and inspecting a tube require a time period of at least one week to complete. Therefore, if the pilger mill process is operating in a defective manner, the defect may not be discovered until a week later. This means that a pilger mill may be operating defectively for a substantial period of time before corrective actions are taken. During the time required to detect the defect, many defective tubes may be generated. This causes waste and increases the cost of manufacturing zirconium tubes.
In practice, a pilger mill operator-a human-monitors operation of the mill. Based upon the operator's experience and expertise, the operator adjusts the mill so that higher quality tubes are manufactured. These adjustments may, for example, include the spacing of the rolls, i.e. the roll separation, the speed of roll rotation, the position of the mandrel, and rate of lubrication injection into and between the mandrel and the ingoing tube. Known systems, therefore, are highly dependent upon the experience and expertise of a human operator.